An engine comprising fuel injectors arranged such that a fuel is injected directly into combustion chambers, is known. In such an engine, it is also known that a combustion product (i.e. a substance derived from the combustion of the fuel) deposits on an injection hole outlet adjacent wall face of the fuel injector (i.e. a fuel injector wall face adjacent to the outlet of the fuel injection hole of the fuel injector). In the case that combustion products deposit on the injection hole outlet adjacent wall face, even when a command is given to the fuel injector for making the injector inject a desired amount of fuel, the fuel of the desired amount may not be injected from the fuel injector. Further, when the fuel of the desired amount is not injected from the fuel injector, the output property and the exhaust gas property of the engine may decrease. In the fuel injection control device of the engine described in the Patent Document 1, when the amount of combustion products depositing on the injection hole outlet adjacent wall face (hereinafter, the combustion product depositing on the injection hole outlet adjacent wall face, will be referred to as—deposit—and the amount of the deposit will be referred to as—deposit amount—) is equal to or larger than the base amount, the fuel injection is controlled such that the deposit is removed from the injection hole outlet adjacent wall face.
In the fuel injection device described in the Patent Document 1, the deposit amount is used for judging if the deposit should be removed from the injection hole outlet adjacent wall face. Therefore, in the Patent Document 1, it is necessary to estimate the deposit amount. When the amount of the fuel actually injected from the fuel injector will be referred to as actual fuel injection amount, the amount of the fuel required to be injected from the fuel injector will be referred to as required fuel injection amount and the command value given to the fuel injector for making the fuel injector inject the fuel of the required fuel injection amount when the deposit amount is zero will be referred to as fuel injection command value, in the Patent Document 1, from the knowledge that the actual fuel injection amount is smaller than the required fuel injection amount when there is the deposit on the injection hole outlet adjacent wall face and the actual fuel injection amount becomes smaller than the required fuel injection amount as the deposit amount becomes large, the deposit amount is estimated on the basis of the difference between the actual and required fuel injection amounts when the actual fuel injection amount is smaller than the required fuel injection amount. In this case, it should be noted that it is estimated that the deposit amount is large as the difference between the actual and required fuel injection amounts is large.